Quantitative analysis of acetic acid and ethanol in aqueous solutions and in fermentation solutions using attenuated total reflection fourier transform infrared (ATR FTIR) spectroscopy

The Palestinian economy relies mainly on the agricultural sector. Palestinian farmers suffer from crop failure, especially dates. One successful way to reduce their losses is to convert poor quality fruits into valuable products such as acetic acid and ethanol through fruit fermentation. It is important for them to analyze the percentage of ethanol and acetic acid in their products in simple, fast, easy, cheap, without sample preparation, robust, accurate and precise method. The objectives of this work are therefore to use an attenuated total reflection fourier transform infrared (ATR FTIR) instrument for quantitative analysis of acetic acid and ethanol in fermentation products. Different solutions of acetic acid in aqueous solutions were prepared in the range of 0.5 to 30% w/w; similarly, different solutions of ethanol in aqueous solutions were prepared in the range of 0.5 to 30% w/w. Infrared (IR) spectra of these solutions were recorded from 4000-400 cm -1 . Calibration curves were constructed by plotting mass% % of ethanol or acetic acid vs. absorbance at a certain wavelength and then choosing the best calibration curve with the highest correlation coefficient. The method was validated by conducting precision and accuracy, as well as specificity, linearity, and range of the method. It was found that the mass% % of acetic acid in aqueous solution can be determined from the equation: mass% % acetic acid = 11.902R – 11.763, where R is the ratio of the absorbance of acetic acid in the sample at 1703.0 cm -1 to the absorbance of pure water at 1703.0 cm -1 . While the mass% % of ethanol in aqueous solution can be determined from the equation: mass% % ethanol = 56.34R – 15.452, where R is the ratio of absorbance of ethanol in the sample at 1087.8 to that at 1636.0 cm -1 . The method has been validated, and results showed that this method for the determination of acetic acid and ethanol is accurate, precise, linear, and selective. FTIR method is a simple, robust, accurate, precise, with no sample preparation step, and fast method for simultaneous determination of acetic acid and ethanol in aqueous solutions, e.g., fermentation products.